Loop network topologies such as Fibre Channel Arbitrated Loop (FC-AL) networks are currently starting to use switch technologies in order to improve bandwidth by taking advantage of the capabilities that spatial reuse can give. In order to do this, trunking is used, where trunking is an extra connection, that allows multiple Host Bus Adapters (HBAs) to use the same FC-AL for data transfer simultaneously; where the switch uses different trunks for different I/O paths, one for each HBA. This concept of inter-switch trunking is well-known in the art and need not be further described here.
The current switch technology is not directly capable of appreciating (or assigning primary and secondary roles to) the trunks to be used dynamically, but rather needs the assignment to be appreciated for it. Herein lies a problem, where the switch technology needs to be informed of the nature of each trunk, such that it can perform this task.
This can be achieved today by assigning certain characteristics to each possible connection. This, however, creates the problem that the nature of the connection is determined in advance rather than determined at the time of connection. Errors in the cabling can therefore cause the trunking to fail, which is very undesirable.
Another alternative is to have a manual appreciation after the cables are assigned. This, however, relies on accurate understanding of the cabled system and as such is prone to operator error and also adds another step in the process where FC-AL does not normally need such a step.
Techniques such as choosing the ‘first connection’ as the primary and the ‘second connection’ as the secondary are flawed, as the way in which this rule may cause the network to behave is dependent both upon time and switch behaviour, which may not be deterministic.